| Risk factor | Odds ratio |
|---|---|
| Prolonged third stage of labor | 7.6 |
| Preeclampsia | 5.0 |
| Mediolateral episiotomy | 4.7 |
| Previous postpartum hemorrhage | 3.5 |
| Twin pregnancy | 3.3 |
| Arrest of descent | 2.9 |
| Soft-tissue lacerations | 2.0 |
| Asian ethnicity | 1.7 |
| Augmented labor | 1.7 |
| Forceps or vacuum delivery | 1.7 |
| Hispanic ethnicity | 1.7 |
| Midline episiotomy | 1.6 |
| Nulliparity | 1.5 |